1. Field of the Invention
The invention relates to radio-frequency-surgical (RF-surgical) snares for endoscopically monitored methods by which tissue in hollow organs, particularly pathological mucosal-submucosal areas or tumors of the gastrointestinal tract, can be ensnared and removed from the wall of the hollow organ by RF-surgical means for diagnostic and/or therapeutic purposes.
2. Description of Relevant Art
It is known that malignant tumors, also known as carcinomas, of the gastrointestinal tract, that is, the oesophagus, the stomach and the colon, cause metastases into other organs and are one of the four most common causes of death worldwide. 1 million new cases and 500,000 deaths are caused every year by malignant tumors of the colon alone, these tumors normally occurring in the mucosa or mucous membrane of the organ concerned through benign changes in the mucosa and then growing cancerously into the layers of tissue located under the mucosa, that is, into the submucosa and the muscularis propria or muscle layer as well as into the blood and lymph vessels located inside these. If a malignant tumor has grown into the blood or lymph vessels, malignant tumor cells may find their way through these vessels into other, and particularly vital, organs and there form metastases which cannot be easily treated or be treated at all. Since efferent blood and lymph vessels already start in the submucosa, earliest possible diagnosis and removal of malignant tumors of the mucosa are the surest means of preventing its proliferation in- and outside the organ wall concerned and/or metastasising into other organs.
If during an endoscopic examination of the gastrointestinal tract pathologically remarkable mucosal areas are found, a diagnostic examination of this mucosal area for carcinomatous components and their proliferation into the submucosa containing the blood and lymph vessels is indicated. For this the mucosal area concerned with the submucosa underneath it must as far as possible be separated from the organ wall en bloc, that is, in one piece and completely, that is, in depth as close as possible to the muscularis propria and planarly at sufficient distance from the pathologically remarkable mucosal area, and removed from the gastrointestinal tract for pathohistological examination. Here it should be noted that the wall of the hollow organs of the gastrointestinal tract, and particularly that of the colon, is at approx. 2 mm very thin, and particularly that the normal mucosa of the colon is only approx. 0.3 mm thick and the normal submucosa located underneath it only approx. 0.3 mm to 0.7 mm thick, while the planar extension of a pathologically remarka ble mucosal area may be several centimeters in diameter.
Pathological mucosal-submucosal areas may in their demand for space spread into the lumen of hollow organs, that is, project from the level of the surface of the normal mucosa, and form what are known as polyps. Pathological mucosal-submucosal areas may however also occur planarly and without projecting from the level of the normal mucosa.
Known methods of separating and removing pathological mucosal-submucosal areas or tumors in the gastrointestinal tract are in particular endoscopic polypectomy (EPE), endoscopic mucosa resection (EMR) and endoscopic submucosal dissection (ESD).
These methods all have the common purpose of completely removing tumors for diagnostic or therapeutic purposes. This purpose is achieved when the pathohistological examination of the removed tissue confirms fulfilment of the criteria of an RO resection according to the UICC classification, i.e. that the EPE, EMR or ESD has removed the whole of the pathological, particularly the malignant, tumor tissue, or that it has been performed in the healthy tissue outside the pathological, particularly the malignant, tumor. With regard to a pathohistological examination of the removed tissue and the spatial assignment of a particularly malignant result in the removed tissue to the respective ectomy, resection or dissection limit on the organ concerned removal in toto and en bloc, that is, totally and in a single piece, is advised and particularly in the case of large or large-area tumors even essential for a safe pathohistological examination and evaluation of the removed tissue with regard to the radicality of the removal of benign and in particular malignant tissue.
By endoscopic polypectomy (EPE) is generally meant a method where a loopshaped RF surgical electrode, known generally as a polypectomy snare, is looped around a polyp to be removed and RF-surgically ectomised or separated in toto and en bloc from the organ concerned or the organ wall. RO polypectomy in toto and en bloc is possible only if a polypectomy snare is placed securely around the base or near to the muscularis propria of the organ wall concerned underneath the polyp to be ectomised and the polyp can be ectomised RF-surgically in toto and en bloc close to the muscularis propria. If a pathological mucosal-submucosal area projects too little or not at all above the normal mucosal-submucosal area, it cannot be securely ensnared or ensnared at all with a polypectomy snare and cannot be ectomised. In such a case one injects, for example, physiological NaCI solution into the submucosa underneath the mucosal area or tumor concerned in order to raise the mucosal-submucosal area concerned far enough above the level of the normal mucosa-submucosa level for a polypectomy snare to be placed around it and for it to be resected RF-surgically as close as possible to the muscularis propria of the organ wall located underneath it. This method is, as already mentioned above, accordingly known as endoscopic mucosal resection (EMR).
Known instruments for EPE and EMR incorporate essentially an RF-surgical snare, a flexible catheter, one or more flexible manipulation wires which extend inside the catheter in an axial direction for pulling out or inserting the snare from or into the distal end of the catheter and to conduct the RF-current needed for RF-surgical removal of the tissue round which the snare is looped and a handle at the proximal end of the catheter, which catheter consists of a slide rail and a sliding member for manually pushing out or pulling in the snares from or into the distal end of the catheter. Disposed on the sliding member is at least one electrical contact for connection to an RF-surgical generator (RF generator). By polypectomy snare is generally meant pars pro toto the whole instrument, including a polypectomy snare integrated into it, and specifically a separate polypectomy snare separate from the instrument. For the sake of clarity, the separate polypectomy snare will in the following be referred to as “snare” for short and the whole instrument, including the snare, as “instrument.” Instruments with a fixedly integrated snare should to avoid hygiene problems and in the absence of adequate cleansing and disinfection facilities be used only once or on the same patient. Instruments with exchangeable snare can be adequately cleaned and disinfected and may therefore be used a number of times or on different patients. This invention accordingly relates both to separate snares and to instruments with an integrated snare.
As regards the technique for applying the snare a distinction is made between symmetrical snares or snares that open and close symmetrically and asymmetrical snares or snares that open and close asymmetrically. For a description of the differences between symmetrical and asymmetrical snares it is practical to consider snares consisting of two snare portions which are connected together to form a loop at their proximal and distal ends.
Monopolar symmetrical snares incorporate two snare portions which are of equal length and which are connected at their proximal ends to the distal end of a manipulation wire and therefore are or can be pushed out of or pulled into the distal end of the catheter at the same time and at the same speed. Consequently the two snare portions must be of the same length, regardless of whether the two snare portions connected together are mirror-image identical or differently shaped or preshaped.
Monopolar asymmetrical snares incorporate two snare portions, one longer than the other. Only the proximal end of the longer of the two snare portions is connected to the distal end of a manipulation wire and can thus be actively pushed out of or pulled into the distal end of the catheter. The shorter snare portion which is mechanically connected at its distal end to the longer snare portion at its distal end can be passively pulled out by the longer snare portion from the distal end of the catheter as far as a stop which is disposed on a stop device disposed at the distal end of the catheter and which acts at the proximal end of the shorter snare portion. Known stop devices are combined with a driving device. Here the longer snare portion is fitted with a mechanical driver which, when the longer snare portion is pulled back from a defined position, also pulls the shorter snare portion into the distal end of the catheter at the same time. This combined stop-driver device is on known asymmetrical polypectomy snares disposed direct at the distal end of the catheter.
Since the introduction of EPE and EMR there has been a wish to remove increasingly large polyps or pathological mucosal-submucosal areas of the gastrointestinal tract for diagnostic and/or therapeutic purposes, and this with a view to pathohistological examination, as already mentioned above, as far as possible in toto and en bloc. However, as the size of the polyps ectomised or mucosal-submucosal areas resected in toto and en bloc has increased, the resulting problems and complications set out below have increased with the use of the snares available hitherto for EPE and EMR and the RF generators available for operating these snares.
One of these problems consists in the fact that particularly with en-bloc separation of large polyps or large-area mucosal-submucosal areas, particularly if through submucosal injection these become even greater than they are already before injection, is the electrical power required for this. Since the RF-surgical cutting effect can then and only then be achieved if between the snare used for cutting and the tissue to be cut electric arcs which burn away the tissue located close to the polypectomy or mucosectomy snare (pyrolysis) occur at sufficiently high RF voltage, the tissue close to the snare must be heated to the boiling temperature of water beforehand so that between the snare and the tissue an electrically insulating layer of water vapour is created in which at sufficient electrical field strength electric arcing then occurs. If this tissue is heated too slowly or with too long a time lag, which it is feared may result in a delay in initial incision, the heat created here may diffuse from the tissue into the adjacent tissue close to the snare and damage the adjacent tissue thermally. If for the abovementioned reason the snare is applied close to the organ wall, the muscularis propria may be thermally damaged by it. Thermal damage to the muscularis propria or even the serosa of a hollow organ of the gastrointestinal tract may result in perforation of this organ and will not infrequently make an open surgical operation necessary.
For a sufficiently lag free initial incision during polypectomy or mucosaresection an RF current of approx. 0.5 amperes per cm of snare length is required. Since RF generators of known RF surgical instruments generate 1.5 to 3 amperes at maximum, only polyps or mucosal-submucosal areas with a maximum diameter in the application area of the snare of approx. 1 to 2 cm—corresponding to an effective snare length of approx. 3 to 6 cm—can be separated en bloc with a sufficiently short initial-incision lag. With larger polyps or mucosal-submucosal areas there is actually no cutting effect at all.
To solve this problem it is disclosed by G. Maslanka in the German patent application publication DE 100 28 413 A1, that the snare, there referred to as “electrode”, or the snare wire, there referred to as the “electrode core”, be lined with an insulating sheath. Here the free electrode surface of the electrode core is in one or more parts of the electrode reduced by a portion of the insulating sheath incorporating a large number of holes. Alternatively the effective electrode surface of the snare electrode can be limited to an area near the electrode tip by insulation-sheathing of the two snare portions. This last was disclosed as early as 1975 by Karl Storz in the German patent application publication DE 2514501 and 1990 by L. F. Doll in U.S. Pat. No. 5,078,716.
The snare as disclosed in DE 2514501 is a bipolar snare comprising two mirror-image-formed snare halves, referred to there as “electrodes.” Here the two electrodes form a snare in that they are connected together at their ends by means of an insulating element and in that the electrodes are provided with an insulating layer along their entire length, with the exception of an area close to the insulating element.
Bipolar snares have, however, not proved satisfactory in clinical applications. One reason for this is the electrically insulating segments at the proximal and/or at the distal end between the two snare portions. For RF-surgical incisions the amplitude of the RF voltage must reach at least 200 volts between an active electrode used for incisions and the tissue to be cut. Since with bipolar instruments 200 volts with opposing polarity or phasing must be reached on each of the two active electrodes at the same time, the electrical insulation segments between the two active electrodes must, particularly at the proximal or distal end of the snare, where the distances between the two electrodes are very short, withstand a voltage amplitude or amplitude difference of at least 400 V. If electric arcing occurs between the two electrodes at these points, these electrodes may melt because of the high temperature of this electric arcing. For this reason bipolar snares have not proved satisfactory in practice.
In the U.S. Pat. No. 5,078,716 titled “Electrosurgical Apparatus for Resecting Abnormal Protruding Growth” a monopolar polypectomy snare is described by example of FIG. 1, the two snare portions of which are proximally with the exception of relatively short segments at the distal end of the snare electrically insulated so that only a relatively short segment at the distal end of the snare is insulated and is thereby RF-surgically effective. Although snares of this kind require less RF current during the initial-incision phase and during the incision phase than snares of the same size without insulation, they have the disadvantage that the RF-surgically effective part of the snare viewed from an endoscope is always behind the polyp, that is, is out of sight, and there is a risk that the distal tip of the snare can perforate the organ wall unmonitored. Avoiding the latter is, amongst other things, the subject of DE 100 28 413 A1. Here the active electrode surface is reduced by sheathing with holes in it. This form of electrode may, however, hinder accurate incision.
Both with electrosurgical instruments in accordance with U.S. Pat. No. 5,078,716 and DE 100 28 413 A1 and coagulating instruments in accordance with DE 25 14 501 the RF-surgically effective electrode surfaces can be disposed only at the distal end of the snare, with the disadvantage that these, seen through an endoscope, are always behind the tissue to be removed and the incision therefore has to be made without visual monitoring, which is a risky process, particularly with large polyps or mucosal-submucosal areas.
A further problem is the placing of the snare around in particular large or oddly shaped polyps or around polyps or mucosal-submucosal areas which have become enlarged through the injection of physiological NaCl solution or other injectables into the submucosa, that is, by submucosal injection, enlarged or oddly shaped polyps or mucosal-submucosal areas. To solve this problem special snare shapes, for example, hexagonal or crescent-shaped snares, and designs, and particularly asymmetrical snares or rotatably symmetrical snares, have been and are being developed, with which these polyps or mucosal-submucosal areas can also be ensnared. However, all these snares for separating the tumor close to the muscularis propria must for the above-mentioned reason not be pressed against the organ wall during RF-surgical incision.
A further problem is the placing and guidance of the snare as close to the organ wall as possible in order to separate the tumor close to the muscularis propria for the above-mentioned reasons. With multi-strand or braided standard snares this is normally not practicable, because these snares are too soft or too flexible for this. To overcome this problem special snares are recommended, such as monofilament snares or flat snares which are so flexurally stiff that they can be pressed firmly against the organ wall or into the mucosa. The use of these snares is, however, hazardous in so far as because of the pressure against the organ wall they can also cut into or even through the organ wall.
A further problem, particularly with large polyps or mucosal-submucosal areas with an abnormally slippery surface may be that the snare slips out of the intended position while being applied or manipulated. Since wide open snares, especially when being placed around flat polyps or mucosal-submucosal areas, cannot or must not be pressed against the organ wall concerned sufficiently firmly, they may, when the snare is closed, slip over the slippery mucous membrane and out of the intended position.
To avoid this problem polypectomy snares are known which are fitted with little claws or spurs or in which the snare wire is folded at a number of points to form small claws or spurs which, when the snare is closed, hook into or grip the tissue to prevent slipping. However, these claws or teeth must not be too long or too large, as otherwise they may prevent the snare from being pulled back into the only approx. 1 mm-wide hole at the distal end of the catheter. On asymmetrical snares claws, hooks or teeth of this kind interfere with the function of the above-described driving device.
Although endoscopic polypectomy and endoscopic mucosaresection are regarded today as clinically established methods, these methods are presumably also because of the above-described problems attended with various complications.
Complications in this regard are in particular bleeding from injured blood vessels, perforation of the organ wall and relapses as a result of incomplete removal of a tumor. The rate of these complications rises, amongst other things, in proportion to the size of the tumor removed (T. Rösch: Endoskopische Mukosaresektion im oberen and unteren Gastrointestinal-Trakt. Dtsch Med Wochenschrift 2004; 129: 126-129 MUPS). Both because of the above-described problems and because of the complication rate rising due to the mean diameter of the tumor the hitherto available abovementioned methods and snares only can only be used to remove polyps or mucosal-submucosal areas in toto and en bloc with a maximum mean diameter of up to approx. 2 cm. With these methods larger polyps or mucosal-submucosal areas can be removed only by a piecemeal technique and often not radically or completely, a circumstance which may result in relapses.
In order to remove in toto or en bloc as closely as possible to the muscularis propria of organ walls large mucosal-submucosal areas which cannot be removed in toto and en bloc safely or at all with available snares and RF generators various endoscopic submucosal dissection (ESD) methods have been and are being developed and some are already being applied clinically. A common feature of these methods is the RF-surgical removal of the mucosal-submucosal area from the organ wall as closely as possible to the muscularis propria with, for example, a needle electrode.
These methods, however, call for a high degree of manual dexterity, experience, constant training, a willingness to take risks and long operating times. So far there have been only a very few experts who practise these methods.